Heretofore, as a method for manufacturing an annular member applied to an inner ring or outer ring of a roller bearing or the like, a process shown in FIGS. 20A to 20E is mentioned. First, by using a round bar member 101 shown in FIG. 20A, a cut billet 102 shown in FIG. 20B is made by any method of press cutting, saw cutting and cutting-off. At this time, in a case where the cut billet 102 is cut out by the press cutting, surface roughness of a cutting section thereof is not acceptable, and accordingly, a crack is prone to occur therein, and a perpendicularity of the cutting section to an axial direction thereof is poor. Therefore, upsetting or end surface correction is performed for the cut billet 102.
Next, as shown in FIG. 20C, the cut billet 102 is subjected to backward extrusion, whereby a backward extrusion billet 103, which forms a top-opened and bottomed cylindrical shape, is formed.
Next, as shown in FIG. 20D, a bottom portion 103a of the backward extrusion billet 103 is penetrated, and a cylindrical member (pipe-like member) 104 is formed.
Next, as shown in FIG. 20E, the cylindrical member 104 is subjected to shear cutting, cutting-off or saw cutting (cutting) over an axial direction thereof, whereby a plurality of annular members (ring-like members) 105 is fabricated.
Here, Patent Literature 1 and Patent Literature 2 disclose a technology regarding the shear cutting mentioned as a technology for cutting the cylindrical member 104 over the axial direction thereof and dividing the cylindrical member 104 into the plurality of annular members. The technology disclosed in Patent Literature 1 and Patent Literature 2 is a technology for bringing a cored bar into intimate contact with an inner circumferential surface of a cylindrical member (pipe-like member) and shearing the cylindrical member (pipe-like member) by using a tapered wedge. Moreover, Patent Literature 3 discloses a technology for cutting the cylindrical member by using an expansion blade as the technology for cutting the cylindrical member (pipe-like member) over the axial direction thereof and dividing the cylindrical member into the plurality of annular members.